An electromagnetic valve disclosed in JP-11-344145A and JP-2001-241563A has two valve bodies each of which operates in series at the valve opening timing to prevent a rapid increase of an opening area through which a fluid flows. As shown in FIG. 12A, when a coil is energized, a first valve body 400 is lifted from a second valve body 410, so that a fluid flows to a fluid passage 420 through a communicating passage 412 formed inside the second valve body 410. Then the second valve body 410 is lifted from a valve seat 422 formed at an opening side of the fluid passage 420 in response to a decrease of a pressure difference between an upstream side and a downstream side of the second valve body 410, and thereby the fluid amount increases due to the increase of the opening area. FIG. 12B discloses how the opening area changes before the second valve body 410 is lifted from the valve seat 422.
However, when the first valve body 400 is lifted from the second valve body 410 and the fluid flows to the fluid passage 420 through the communicating passage 412, pressure-reflected waves arise to the downstream of the fluid passage 420 due to the volume change of the passage. Therefore, as shown in FIG. 13 (pressure of zero indicates atmospheric pressure in FIG. 13), the pressure is apt to change. For example, if the pressure of the fluid passage 420 changes sharply, the second valve body 410 tends to be lifted from the valve seat 422 in the timing other than the suitable timing. Then, the lift timing of the second valve body 410 fluctuates due to the pressure fluctuation. In the electro magnetic valve disclosed in JP-11-344145A and JP-2001-241563A, the lift timing of the second valve body tends to fluctuate because the opening area varies similarly to a change as illustrated in FIG. 12B before the second valve body is lifted.
In the JP-11-344145A, a part of a main valve corresponding to the second valve body as disclosed above protrudes toward the passage side. Therefore, the sharp increase of the fluid amount due to the sharp increase of the opening area can be prevented when the main valve is lifted, so that the pressure change can be prevented. However the fluid flowing into the downstream through the pilot passage formed inside the main valve causes a pressure change to the downstream of the fluid passage when the pilot valve corresponding to the first valve body is lifted. As a result, the lift timing of the main valve tends to fluctuate.